The present invention relates generally to catheters and catheter procedures involving laser energy delivery using fiber optic and other laser delivery systems. More particularly, the invention relates to a steerable catheter and method of use, particularly adapted for laser-assisted transmyocardial revascularization (TMR). The distal tip of a central, hollow flexible center tube for guiding a laser delivery means or other functional device extendable therethrough is deflectable utilizing a semi rigid shim, the shim acted upon by a pull cable for controllably deflecting the distal tip of the steerable catheter in at least one given plane. The steerable catheter can be used in conjunction with a fiber or other laser delivery means advance mechanism, optionally using a depth control mechanism as well.
In the treatment of heart disease, one method of improving myocardial blood supply is called transmyocardial revascularization (TMR), the creation of channels in the myocardium of the heart. The procedure using needles in a form of surgical xe2x80x9cmyocardial acupuncturexe2x80x9d has been used clinically since the 1960s. Deckelbaum. L. I., Cardiovascular Applications of Laser Technology, Lasers in Surgery and Medicine 15:315-341 (1994). The technique relieves ischemia by allowing blood to pass from the ventricle through the channels either directly into other vessels communicating with the channels or into myocardial sinusoids which connect to the myocardial microcirculation.
In the reptilian heart, perfusion occurs via communicating channels between the left ventricle and the coronary arteries. Frazier, O. H., Myocardial Revascularization with Laserxe2x80x94Preliminary Findings, Circulation, 1995; 92 [suppl II]:II-58-II-65. There is evidence of these communicating channels in the developing human embryo. In the human heart, myocardial microanatomy involves the presence of myocardial sinusoids. These sinusoidal communications vary in size and structure, but represent a network of direct arterial-luminal, arterial-arterial, arterial-venous, and venous-luminal connections. This vascular mesh forms an important source of myocardial blood supply in reptiles but its role in humans is poorly understood.
Numerous surgical TMR studies have been performed, including early studies using needles to perform myocardial acupuncture, or boring, to mechanically displace and/or remove tissue. Such studies have involved surgically exposing the heart and sequentially inserting needles to form a number of channels through the epicardium, myocardium, and endocardium to allow blood from the ventricle to perfuse the channels. The early studies using needles showed that the newly created channels were subject to acute thrombosis followed by organization and fibrosis of clots resulting in channel closure. Interest in TMR using needles waned with the knowledge that such channels did not remain open. However, interest in TMR procedures has recurred with the advent of medical lasers used to create TMR channels. Histological evidence of patent, endothelium-lined tracts within laser-created channels shows that the lumen of laser channels can become hemocompatible and resists occlusion. A thin zone of charring occurs on the periphery of the laser-created channels through the well-known thermal effects of optical radiation on cardiovascular tissue. Additionally, recent histological evidence shows probable new vessel formation adjacent collagen occluded transmyocardial channels, thereby suggesting benefits from TMR with or without the formation of channels which remain patent.
Surgical TMR procedures using laser energy have been described in the prior art. U.S. Pat. No. 4,658,817 issued Apr. 21, 1987 to Hardy teaches a method and apparatus for surgical TMR using a CO2 laser connected to an articulated arm having a handpiece attached thereto. The handpiece emits laser energy from a single aperture and is moved around the surface of the heart to create the desired number of channels. U.S. Pat. No. 5,380,316 issued Jan. 10, 1995 to Aita et al. purports to teach the use of a flexible lasing apparatus which is inserted into the open chest cavity in a surgical procedure. A lens at the distal end of the flexible apparatus is used to focus laser energy, and the apparatus is moved about the surface of the heart to create the desired number of channels.
The foregoing discussion relates to surgical procedures, i.e. procedures which access the heart surgically, either via open heart surgery, or perhaps by minimally invasive surgical (MIS) methods if the design and size of the distal ends of the hand pieces are suitable for use in an MIS site. However, since TMR most often involves creating channels through the endocardium into the lower left chamber of the heart, it is desirable to create TMR channels in a percutaneous procedure, i.e. by extending a catheter apparatus through the vasculature into the ventricle and creating the channels through endocardial surfaces and into myocardium. Performing such percutaneous TMR is desirable for a number of reasons. Percutaneous catheter procedures are typically less traumatic to the patient compared to surgical procedures. Adhesions between the pericardial sac and epicardium are eliminated. Percutaneous TMR with a catheter apparatus also offers an alternative solution to persons who are not candidates for surgical procedures.
Because TMR procedures generally involve creating a plurality of channels within the myocardium, performing the procedure percutaneously requires the ability to steer a catheter apparatus through the vasculature and maneuver the apparatus within the ventricle of the beating heart as rapidly as possible to create the channels without subjecting the heart to the undue stress of a lengthy procedure. Additionally, the ability to control and stabilize the catheter apparatus against the beating heart wall while creating channels with a laser is desirable for percutaneous procedures to ensure creation of channels as desired and to ensure that the laser is fired only within the myocardial tissue. MR channels should be spaced and grouped appropriately to achieve the desired result without weakening or rupturing the heart muscle.
The early myocardial acupuncture procedures were not performed percutaneously. The Hardy CO2 laser delivery system described above is rigid, relatively large, and not adaptable for percutaneous use. The Aita ""316 patent does not suggest a method for percutaneous use of the laser delivery device described therein for surgical use.
U.S. Pat. No. 5, 389,096 issued Feb. 14, 1995 to Aita et al. purports to teach one method of percutaneous TMR using an elongated flexible lasing apparatus with control lines and a focusing lens structure at the distal tip. However, the method uses pressure applied manually to attempt to stabilize the apparatus against the wall of the heart, and no central, hollow passageway is described. No handle structure, modular or otherwise, is described nor are deflection, deflection components or a floating center tube.
Several prior art patents describe the use of catheters within the ventricle for percutaneous treatment of ventricular tachycardia. Such devices have a means to locate an arrhythmia site and ablate the site, at or just below the ventricle surface, using an electrode device or laser energy. U.S. Pat. No. 5,104,393 issued Apr. 14, 1992 to Isner teaches a catheter apparatus having a guiding Y-shaped sheath and guide catheter assembly for introducing an optical fiber into the ventricle. Positioning is described to enable a single burst of laser energy from a single aperture to ablate the site. However, positioning or specific steering means sufficient to create one or more TMR channels is not described or suggested.
U.S. Pat. Nos. 5,255,679 issued Oct. 26, 1993 and 5,465,717 issued Nov. 14, 1995 to, respectively, Imran and Imran et al., disclose non-laser, basket-shaped catheter apparatus for mapping and/or ablation of arrhythmia sites within the ventricle. A pull cable is used to expand the basket portion within the ventricle, and a plurality of electrodes on the arms of the basket are used for ablation. The basket device is designed to place the electrodes on the ventricle wall. Although the device allows for a fairly extensive mapping procedure without repositioning, no positioning means is provided for a laser delivery system to allow creation of TMR channels.
U.S. Pat. No. 5,114,402 issued May 19, 1992 to McCoy teaches a maneuverable distal apparatus with a temperature activated material of construction which, upon heating to a predetermined position, will assume a predetermined, memorized shape, and which upon cooling, will assume a different shape by action of a spring element urging the apparatus into the different shape.
U.S. Pat. No. 5,190,050 issued Mar. 2, 1993 to Nitzsche teaches a steerable catheter with a handle and a tube, the distal tip of which may be selectively curved by controllably moving one of three flat, sandwiched shims relative to the others by manipulation of a handle portion. However, deflection control requires the use of multiple shims, and no mechanism for integrated or otherwise fiber advance means is taught.
U.S. Pat. No. 5,358,479 issued Oct. 25, 1994 to Wilson, hereby incorporated herein in its entirety by reference, teaches another steerable catheter with a handle and a center tube, the apparatus having a single elongated, substantially flat shim spring mounted within the tip of the catheter tube, the shim having at least one transverse or lateral twist which causes the tip of the catheter tube to assume a desired curvature. However, Wilson does not teach the use of a hollow catheter for delivery of laser energy or any other functional device, nor does it contemplate the use of a floating center tube.
The use of superelastic and/or shape memory materials is widely known. Structure and Properties of Tixe2x80x94NI Alloys- Nitinol Devices and Components, Duerig et al., In Press, Titanium Handbook, ASM (1994) In general, binary compositions of Nickel (Ni) and Titanium (Ti), yield alloys with shape memory and superelastic properties. These alloys are commonly referred to as Nixe2x80x94Ti, nitinol, and other industry names. Their precise physical and other properties of interest are extremely sensitive to the precise Ni/Ti ratio used. Generally, alloys with 49.0 to 50.7 atomic % of Ti are commercially available, with superelastic alloys in the range of 49.0 to 49.4%, and shape memory alloys in the range of 49.7 to 50.7%. Due to a rapid decrease in the ductility of the material, binary alloys.with less than 49.4 at. % Ti are generally unstable. In general, these types of materials exhibit hysteresis, defined as a phenomenon exhibited by a system whose state depends on its previous history, and illustrated diagrammatically by the familiar upper and lower curves which meet at the ends and define an area under the curves. In the case of solid materials undergoing elastic hysteresis (as opposed to magnetic or electrical hysteresis), the curves are related to stress necessary to cause deformation or otherwise overcome existing stress in prestressed materials.
Properties of these materials change significantly as their respective xe2x80x9cphase transformation temperaturesxe2x80x9d are approached. In general, at lower temperatures, these alloys will exist in a martensite state characterized as hard and easily deformed. However, in austenite, the high temperature phase, the alloys have a much higher yield and flow stresses. The addition of small amounts of third elements in the alloy can also have very significant effects on performance of the materials. Elements including but not limited to oxygen (O), nitrogen (N), iron (Fe), aluminum (Al), chromium (Cr), cobalt (Co) vanadium (V), zirconium (Zr) and copper (Cu), though having various effects on the Nixe2x80x94Ti matrix, can have the tendency to increase strength, increase stiffness, control hysteresis and/or decrease or increase phase transition temperatures.
Nixe2x80x94Ti products are commonly used in the form of cold drawn wire or as barstock. Tubing is also available. The toxicity of the alloy or the solubility or other compatibility with the biological environment in which catheter equipment is used is an important consideration. The alloys are commonly used in a cold worked and partially annealed condition. The partial anneal does not recrystallize the material but does bring about the onset of recovery processes. The extent of the post-cold worked recovery depends upon many aspects of the application, such as the desired stiffness, fatigue life, ductility, recovery stress, etc. Nixe2x80x94Ti is difficult to join since most mating materials cannot tolerate the large strains experienced by Nixe2x80x94Ti. Most connections will rely on crimped bonds. Although Nixe2x80x94Ti can be brazed or welded to itself with relative ease, such as by resistance and with TIG methods, brazing or welding to other materials is difficult though proprietary methods do exist and are practiced in large volumes, for example in the production of eyeglass frames.
For the purposes of this disclosure, a distinction between superelastic materials and shape memory materials is made. Superelasticity refers to the highly exaggerated elasticity, or springback, observed in many Nixe2x80x94Ti alloys deformed at a specific temperature. The function of the material in many of such cases is to store mechanical energy. Though limited to a rather small temperature range, these alloys can deliver over 15 times the elastic motion of a spring steel, i.e., withstand a force up to 15 times greater without permanent deformation. Shape memory materials will refer to those materials which can be deformed, but which will freely recover their original shapes during heating, often utilizing electrical resistivity, or which will develop a large recovery stress when recovery is prevented. With regard to the present invention, it will be understood that the transition temperature of materials must, in general, be somewhat above body temperature.
U.S. Pat. No. 3,890,977 issued Jun. 24, 1975 to Wilson teaches kinetic memory electrodes, catheters and cannulae. These devices incorporate a material, such as a Nixe2x80x94Ti alloy, having heat-activated mechanical memory properties. The device is formed into an operative shape at a high temperature. Then, at a low temperature below its transitional temperature, it is reformed into a shape for ease of insertion into a guide catheter or the like or otherwise through a portion of a patient""s vasculature or other body lumen. When located in the organ or other desired region, those portions of the device constructed using such shape memory materials are heated to above their transitional temperatures, using electrically resistive elements, thereby returning the catheter to its original annealed anchoring or proper locating shape. An important drawback of the Wilson apparatus is that heat must be applied to the catheter tip. Complicated construction and electrical power distribution must be considered.
As can be seen from a description of the prior art above, percutaneous TMR steerable catheters are virtually unknown with the exception of the catheter briefly described in the ""096 Aita patent. There is a need in the art for a percutaneous TMR steerable catheter which has means for easily steering, positioning and repositioning the steerable catheter on the ventricle wall, and having a port for a laser delivery means to enable rapid creation of one or more appropriately grouped and spaced TMR channels.
Thus, it is an advantage of the present invention to provide a steerable catheter and method of use for percutaneous and other intra-vascular procedures, including TMR, or any stimulation procedure, which overcomes the limitations of the prior art.
It is a further advantage of the present invention to provide a steerable catheter capable of being guided into a heart chamber and used therein for creating a plurality of TMR channels controllably and efficiently.
It is a further advantage of the present invention to provide an elongated steerable catheter for placement within a heart chamber, organ aperture or other body opening, the steerable catheter having at least one center tube with hollow passageway extending therethrough, the center tube for guiding a laser delivery means or other functional device to selected surfaces of the heart chamber, organ aperture or other body opening for laser or other treatment thereon, particularly adapted for laser-assisted transmyocardial revascularization (TMR).
It is yet a further advantage of the present invention to provide a percutaneous steerable catheter which can be positioned securely into a selected position within the left ventricle, or other body opening or cavity.
A further advantage of the present invention is to provide a steerable catheter to enable creation of a plurality of appropriately grouped and spaced TMR channels on a selected surface within a body cavity or organ quickly and safely.
Yet an additional advantage of the present invention is to provide a modular steerable catheter system capable of being assembled and operated as desired, comprising one or more modular assemblies which can be coupled together for operation in unison, including but not limited to a central, modular steerable catheter with a deflectable end portion, a modular fiber advance handpiece unit, and other functional devices including-fiber advance depth control mechanism, visualization means, etc.
Therefore, to summarize, an elongated steerable catheter for placement within a heart chamber, organ aperture or other body opening and having at least one center tube with hollow passageway for guiding a laser delivery means or other functional device to selected surfaces of a heart chamber, organ aperture or other body cavity for laser or other treatment thereon, particularly adapted for laser-assisted percutaneous transmyocardial revascularization (TMR), is disclosed herein. The steerable catheter has a handle portion at its proximal end and a controllably deflectable portion at its distal end.
The elongated center tube has a distal end, in the region where a curvature is to be formed, and a shim anchor sleeve is slidably disposed over the center tube. The shim anchor sleeve is attached to the inside wall of the outer jacket. A bendable shim, member extends between the distal tip of the steerable catheter and the sleeve surrounding the center tube. Opposite the shim is a guide for a pull cable, the pull cable attached to the distal end of the steerable catheter and extending through the guide to the handle. Thus, the shim is maintained radially opposite the pull cable with the center tube in between.
An outer jacket has, in a preferred embodiment, distinct sections of different stiffness or durometer. One or more distinct sections of material of differing stiffness or durometer can be used. Junctions between the sections of different stiffness or durometer can be discrete and clearly defined, or they can blend smoothly or get more or less flexible gradually. A distal, more flexible portion is coupled to a proximal, stiffer portion. The shim anchor sleeve is coupled to the outer jacket at or near the junction of two portions of the outer jacket. Thus, the center tube moves freely through the shim anchor sleeve.
Adjacent the handle, the proximal outer jacket portion terminates at the catheter base. The pull cable extends through the catheter base, through a deflection housing tube, and terminates in a cable stop. Rotation of a deflection knob threadably mounted onto the deflection housing tube will cause the pull cable to be pulled backward, or the outer jacket to be pushed forward, relative to each other, thereby inducing deflection of the distal end of the steerable catheter.
The elongated steerable catheter is designed to be placed into the vasculature of the patient and steered therethrough until the distal tip is adjacent a selected portion of tissue, such as on an endocardial surface within the left ventricle. Thus, the distal tip of a laser delivery means, such as an optical fiber or fiber bundle or other functional device, can be extended through the center tube of the steerable catheter such that its distal tip comes into contact with the selected surface structure for treatment thereon. With regard to TMR therefore, the laser delivery means can be controllably advanced through the steerable catheter for creating one or more TMR channels. Furthermore, with regard to non-laser TMR, a cannula or trocar assembly may be extended through the steerable catheter into the tissue of the left ventricle, with or without use of a mechanical piercing tool.
In a preferred embodiment, the invention is a modular steerable catheter system capable of being assembled and operated as desired, comprising one or more modular assemblies which can be coupled together for operation in unison, including but not limited to a central, modular steerable catheter with a deflectable end portion, a modular fiber advance handpiece unit, and other functional devices including fiber advance depth control mechanism, visualization means, drug delivery apparatus, etc.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.